Journal of Natural P&s Vol. 5 1 , NO.4,pp. 769-770, Jul-Aug 1988
769
X-RAYSTRUCTURE OF CYF'ERENOIC ACID FROM CROTON CRASSlFOLlUS SUPARB BOONYARATAVEJ,
.%PHON ROENGSUMRAN,
Department of Chemistry, Chulalongkm University, Bangkok 10500, Thailand ROBERT B.
BATES, RICHARDB. ORTEGA,and
AMOW PETSOM
Department of Chemistry, University of Arizona, Tucson, Arizona 85721
As part of our investigation of medicinal plants of the genus Croton (Euphorbiaceae) (l), we wish to report the isolation of cyperenoic acid [11 from Croton crassiflius Geisel and its characterization by X-ray diffraction. This substance, first prepared by oxidation of cyperenol (2), has also been found recently as a natural product in Sandwithia guyanensis (Euphorbiaceae) and characterized by nmr (3). Our X-ray study confirms the structure (except for absolute configuration) and makes available the atomic coordinates (Table 1). The two independent molecules in the unit cell are hydrogen-bonded to each other in the usual carboxylic acid dimer fashion (Figure 1; the intermolecular hydrogen-bonding 0 1 4 2 distances are both about 2.6 A). The molecules have similar chair cyclo-
hexane conformations; the largest conformational difference between the two occurs in the rotation about the C 1 410 bond: torsion angle C8a-C 1-C 10-02 is +5O in molecule 1 but -7" in molecule 2. The observed negative optical rotation shows the absolute configuration of 1 from this new source to be the same as that from other sources (2,3); we also reduced the acid 1 with LiAIH4 to levorotatory cyperenol to confirm this. n
1
TABLE1. Atomic Coordinates and Their ESDs. Molecule 1
Atom
0-1 0-2 c-1 c-2 c-3 C-3a c-4 c-5 C-6 c-7 c-8 C-8a
c-9
c-10 c-11 c-12 C- 13
Molecule 2
x
Y
z
x
Y
z
.783( 1) .535(1) .684(2) .838(2) .804(2) .6 17(2) .541(2) .358(2) .269(2) .357(2) .397(2) .563( 1) .533(2) .675(2) .622(3) .533(2) .609(2)
.2468(7) .2704(7) .115( 1) .05 2( 1) -.029(1) - .038( 1) -. 134( 1) -. 1 2 31) - .079( 1) .012(1) .101(1) .0677(9) -.023(1) .2 18(1) -. 154(2) -. 124(1) .065(1)
.3936(3) .4270(3) .4488(5) .4525(5) .4941(5) .4973(4) .4689(5) .4649(5) .5075(6) .532 l(5) .4932(5) .4737(4) .5485(5) .4222(5) .4208(7) .5798(6) .5774(6)
.523(1) .741(1) .595(2) .45 l(2) .502(2) .638(2) .561(2) .68 5(2) .855(2) .907(2) .861(2) .692(2) .801(2) .620(2) .398(2) .794(2) .866(2)
.4509(7) .40 17(7) .559( 1) .637(1) .731(1) .685(1) .654(1) .588(1) .62 l(2) .656(1) .558( 1) .585(1) .747(1) .469(1) .595(1) .844( 1) .787(1)
,376113) .3326(3) .3080(5) .3131(5) .28 10(5) .2473(4) .1952(5) .165 l(6) .1698(6) .2212(5) .2557(5) .2727(4) .2392(5) .3410(5) .1988(6) .2046(6) .2869(6)
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Journal of Natural Products
[Vol. 5 1, No. 4
with 5% NaOH, and the aqueous solution was acidified with HCI and extracted with EtlO. Evaporation of the Et,O and Si gel chromatography of the residue, eluting with 25% CHClJ hexane, gave cyperenoic acid 111.3.5 g, mp 166168”, {a]’5D-7.70 (CHCI,, c=2.0); uv A max 238 nm (E 13764); ir 1649, 1673 cm-’; nmr as reported in the literature (3). X-RAY S T U D Y . ’ < , ~ H ~ ~234.3 ~ ~ , g/mol, orthorhombic, ~2,2,2,,a=8.106(2),b= 12.357(5), r=27.440(9) + , Z = 8 , D,= 1.13 g/cm’; MoKa, A = 0.7 1073 A. Crystal 0.20 X 0.25 X 0.50 rnm, Synrex diffractometer, 28 max = 45”, 1024 of 2093 reflections with I > 2.50(Z) used in refinement. Structure solved using MULTANSO ( 4 ) . Final full-matrix refinement (137 parameters) of non-hydrogen atoms (isotropic temperature factors, bydrogen atoms in calculated positions with 5.0 A’ temperature factors) using SHELX (5) gave R = 0.094. ACKNOWLEDGMENTS We thank the National Research Council of Thailand for financial aid. LITERATURE CITED 1.
FIGURE1. ORTEP drawing of the two independent molecules of 1with 30% probability spheres for non-hydrogen atoms and arbitrarily small spheres for the hydrogen atoms of molecule 1. The dashed line indicates a hydrogen bond.
2. 3.
4.
EXPERIMENTAL Dried roots of C. rrassifolius (10 kg; voucher specimen # 16306, Royal Forest Department Herbarium, Ministry of Agriculture and Cooperative, Bangkok 10900, Thailand) were extracted with EtOH, and the EtOH solution was extracted with hexane. The hexane solution was extracted
5.
S. Roengsumran, W . Luangdilok, A. Petsom, S . Praruggamo, and s. Pengprecha, J . Nut. Prod., 45, 772 (1982). S.B. Nerali and K.K. Chakravarti, Tetruhedron Lptt., 2447 (1967). H . Jacobs, S.S. Lachmansing, F. Ramdayal, S. McLean, F.V. Puzzuoli, and W.F. Reynolds, J . Nut. Prod., 50, 835 (1987). P. Main, S.J. Fiske, S.E. Hull, S.E. Lessinger, G . Germian, J.P. Declercq, and M.M. Woolfson, “MULTAN80. A System for the Automatic Solution of Crystal Structures from X-ray Diffraction Data,” Universities of York, England, and LouvainLaNueve, Belgium, 1980. G.M. Sheldrick, “SHELX76. Program for Crystal-structure Determination,” University of Cambridge, England, 1976.
Reiziwd 15 June 1987
‘Atomic coordinates for this structure have been deposited with the Cambridge Crystallographic Data Centre and can be obtained on request from Dr. Olga Kennard, University Chemical Laboratory, Lensfield Road, Cambridge CB2 IEW, UK.
